利用4-硝基苯乙炔於水相中引發可見光誘導的自由基聚合反應

Abstract

在本實驗室先前研究中，我們發現將 4-硝基苯乙炔 (4-NA) 修飾於半導體氧化亞銅 (Cu2O) 表面後，能有效催化水相中N,N-二甲基丙烯醯胺 (DMA) 的光聚合反應。進一步研究指出，即使不倚賴半導體材料，單獨使用含硝基芳香環結構的有機分子，也展現出啟動自由基聚合的潛力。 基於此發現，本研究進一部探討4-硝基苯乙炔 (4-NA) 是否能作為一種可回收、無金屬添加的水相光引發劑，針對多種具三級胺結構的醯胺類單體 (如N,N-二甲基丙烯醯胺、4-丙烯醯嗎啉、N,N-二乙基丙烯醯胺) 及常見水溶性單體進行聚合實驗，並藉由轉化率與反應性差異，推論其可能的光引發機制。 實驗結果顯示，僅有三級胺類單體 (N,N-二甲基丙烯醯胺、4-丙烯醯嗎啉) 在4-硝基苯乙炔 (4-NA) 光激發後具聚合活性，推測其可能與激發態4-硝基苯乙炔發生電子轉移，生成α-胺基烷基自由基 (α-aminoalkyl radical)，進而加成至單體雙鍵並啟動聚合反應。為佐證此推論，我們進一步利用密度泛函理論 (DFT) 模擬激發態過程，並計算電子轉移與自由基加成步驟的能量變化。特別針對N,N-二甲基丙烯醯胺及4-丙烯醯嗎啉的α-胺基烷基自由基加成步驟執行本徑反應座標 (IRC) 追蹤，成功建立完整的能量路徑與合理的反應能障。此外，透過引入可逆加成－斷裂鏈轉移聚合 (RAFT) 策略，初步觀察到聚合反應之分子量可隨轉化率調控，且分子量分佈趨於狹窄，顯示本系統具備進一步發展為光控可逆－失活自由基聚合 (RDRP) 之潛力。 綜合而言，本研究驗證了以4-硝基苯乙炔作為綠色有機光引發劑的可行性，並揭示其可在無金屬的條件下引發水相聚合反應，對於未來開發環境友善之光控聚合系統提供了嶄新方向。

In our laboratory’s previous research, we found that surface modification of cuprous oxide (Cu2O) nanoparticles with 4-nitrophenylacetylene (4-NA) can effectively catalyze the photopolymerization of N,N-dimethylacrylamide (DMA) in aqueous solution. Further investigations revealed that even in the absence of semiconductor materials, organic molecules containing a nitroaromatic structure alone also exhibit potential in initiating radical polymerization. Building upon this finding, this study explores the feasibility of using 4-NA as a recyclable, metal-free photo-initiator for aqueous-phase polymerization. We conducted polymerization experiments with various amide-based monomers bearing tertiary amine groups (e.g., N,N-dimethylacrylamide, 4-acryloylmorpholine, N,N-diethylacrylamide) and other common water-soluble monomers. Differences in conversion rates and reactivity were analyzed to infer the possible photo-initiation mechanism. The results show that only tertiary amide monomers (N,N-dimethylacrylamide and 4-acryloylmorpholine) exhibited polymerization activity under 4-NA photoexcitation. We propose that this is due to an electron transfer from the monomer to the excited-state 4-NA, generating α-aminoalkyl radicals that subsequently add to the monomer’s double bond, initiating polymerization. To support this hypothesis, density functional theory (DFT) was employed to simulate the excitation process, and energy changes during electron transfer and radical addition were calculated. In particular, intrinsic reaction coordinate (IRC) calculations were carried out for the α-aminoalkyl radical addition step for N,N-dimethylacrylamide and 4-acryloylmorpholine, successfully establishing a complete energy profile and a reasonable activation barrier. In addition, by incorporating a reversible addition–fragmentation chain transfer (RAFT) strategy, preliminary results revealed that the polymer molecular weight could be regulated as a function of monomer conversion, accompanied by relatively narrow molecular weight distributions, indicating the potential of this system to be further developed into a light-controlled reversible-deactivation radical polymerization (RDRP) platform. In conclusion, this study demonstrates the potential of 4-NA as a green, metal-free organic photo-initiator capable of initiating aqueous-phase polymerizations. This work offers a promising strategy for developing environmentally friendly photo-controlled polymerization systems.